1. Field of the Invention
The present invention relates to an internal combustion engine and, more particularly, to a torch-ignition type internal combustion engine having a pre-combustion or trap chamber for the torch-ignition of a charge of an air-fuel mixture fed into a main combustion chamber of the engine.
2. Description of the Prior Art
Torch-ignition internal combustion engines of the type referred to above were already known in the art. This type of internal combustion engines has its maximum merit in that the production of harmful components at the stage of the combustion of an air-fuel mixture is minimized. For this purpose, the internal combustion engines of the type concerned have heretofore been provided with various arrangements and constructions. The torch-ignition internal combustion engines having any of these arrangements and constructions had a common and general characteristics that the engine performance was greatly influenced by the shape of the trap chamber, the size and orientation of a torch aperture or aperture and the position of a set of electrodes of a spark plug. The factors of the engine performance which were influenced most were the ignitability and torch effect.
In the prior art torch-ignition type internal combustion engines, it was usual that the trap chamber was provided with a single torch aperture disposed at the end thereof adjacent to the main combustion chamber and open to the main combustion chamber whereas a set of electrodes of a spark plug was disposed within the trap chamber at the inner part thereof remote from the torch aperture. Any thoughtful consideration was not made with respect to the positional relationship between the torch aperture and the plug electrodes.
It is the inventors' understanding that, with the positioning of the plug electrodes employed in the prior art, the residual gases produced in the preceding combustion stroke and retained in the trap chamber were forced into the inner part of the trap chamber by an air-fuel mixture introduced through the torch aperture into the trap chamber by the upward movement of the piston on compression stroke. At the ignition time, the residual gases were thus retained in the inner part of the trap chamber to form a stratum in the vicinity of the plug electrodes, which presumably adversely affected the spark-ignition of the mixture in the trap chamber. It was observed by the inventors that the ignitability was decreased particularly at a light-load engine operating condition with a resultant poor engine drivability.
With the positioning of the plug electrodes of the prior art, moreover, the front face of the combustion flame produced by a spark-ignition in the trap chamber proceeded from the inner part thereof toward the torch aperture on the combustion stroke. Thus, the amount of the air-fuel mixture which existed between the trap chamber inner part and the torch aperture was forced out of the trap chamber through the torch apertures by the combustion flame while the mixture was still in the unburnt state with a result that the torch effect was very small or low.